Monday, April 23, 2012

They Grow Up So Fast!

The eaglets in Decorah are 27, 26, and 24 days old. Their darker second down has been in for days, and pinfeathers are beginning to show on the edges of their wings, signaling the emergence of their first juvenile contour feathers. Here is how it works. Each feather arises from a feather follicle in the skin. The pin feathers, or feather follicles, contain undeveloped contour feathers. As the contour feathers develop and emerge from their follicles, they push the down feathers off. The down will remain attached to the contour feathers until it rubs off.

Other changes: the eaglets are more proficient at walking and pooping. They are a lot bigger, although their growth curves (when expressed in weight gain per day) will begin slowing sometime in the next three to six days. The overall size of their footpads should already have started slowing down but the growth of their juvenile contour feathers is just taking off : like many animals, parts of the eaglets' bodies grow at different rates.

If human children play house, the eaglets are playing nest. We've seen the eaglets tussle with cornhusks, move debris around the nest, nibble on everything from food to mom's tailfeathers, 'attack' prey, and explore. Socially, they spend a lot of time interacting with one another and with their parents: they alternately dominate and cuddle, observe Mom and Dad (especially when food is involved), and 'help' with nest chores. This behavior is all part of their growth and development. We sometimes think of play as being unimportant or trivial, but play lets young animals 'practice' the skills they need for adulthood, cements bonds between players, and is pleasurable to those playing.
Here are some videos that show our eaglets growing, playing, and practicing:

We've been asked how soon we can tell if the eaglets are male or female. The short answer is that we can't tell for sure unless we capture them and take measurements or a blood test. Having said that, Gary Bortolotti notes that sexual dimorphism begins to appear in some variables after 20 days of age. Initially, size depends more on hatch order than anything else, but after 20 days, gender begins to play a role. Females are bigger than males and have correspondingly wider wingspans, bigger feet, and thicker tarsi. Without proper measurements we are speculating, but speculation is part of the fun.

Bob is anticipating that fledge will happen mid-June: a little less than two months from now. Over the next few weeks, we'll see the eaglets get bigger. Dark brown juvenile feathers will replace their fuzzy grey down and we'll see even more wingercizing and play as they transition from nestlings to flighted hunters. Have fun watching!

We are also waiting for the Great Spirit Bluff Peregrine falcon nest to begin hatch on May 2nd, and the Turkey vultures to lay sometime between May 1 and May 7. There will be a lot to see, laugh at, and learn from.
Things that helped me learn about and write this post:

3 comments:

I am a science teacher for pre-kindergarten through 4th graders in Oak Ridge, TN. This is our second year to watch the Decorah eagles, and my 4th graders are so interested in what they are learning that I've turned it into a research project for them. They posed questions and I have used the ustream site, your blog, and the Journey North site to help them find answers. Thanks you so much for all the information you have provided. I am as excited as my kids about all we are learning. There are a few questions I have not been able to find answers to on the sites we are using. Would you mind if I ask you a few? They would be thrilled if a real Raptor Resource person answered some of their questions. Thanks again for all the work you do!

I'm a 4th grade teacher also and my students have loved watching the eagles too. I did a research project with my students. I gave them questions about eagles and they used the laptops to find the answers. We also made posters and watched the PBS documentary. They are little eagle experts.

Welcome to RRP's Blog!

Established in 1988, the non-profit Raptor Resource Project specializes in the preservation of falcons, eagles, ospreys, hawks, and owls. We create, improve, and directly maintain nests and nest sites, provide training in nest site creation and management, and develop innovations in nest site management and viewing that bring people closer to the natural world. Our mission is to preserve and strengthen raptor populations, expand participation in raptor preservation, and help foster the next generation of preservationists.